[vegipete]

You might get some ideas looking at <http://www.zaber.com>
Or you might get a heart attack from the prices.

[RCaffin]

You might get some ideas looking at <http://www.zaber.com>
Or you might get a heart attack from the prices.

More likely to get a heart attack from the specs: A-LAR-E series: Backlash: <255 microns, or <0.255 mm. What we might call in the CNC world a rattling good fit, with an emphasis on the rattle.

You want accuracy over 4"? Linear motor with optical grating feedback, or if you can afford it, laser interferometer feedback. Both are $$$. You will also need an expensive air conditioner.

Cheers
Roger